Rheumatoid factors are autoantibodies of IgM, IgG, IgA or even IgE class which recognise antigenic determinants on the Fc region of IgG. Remarkably, the exact nature of the antigenic determinants is still not recognised. Since the rheumatoid factor is detected in the presence of a vast excess of IgG in the serum, the antigen which is detected is often referred to as altered IgG. An alternative explanation is that the anti-IgG antibodies are of low affinity and are only detected on aggregated antigen (latex particles in our assay). Rheumatoid factor (usually IgM) is present in approximately 70% of patients with RA. Higher levels and the presence of IgG and IgA RFs correlate with more severe disease. The assay that we use is supposed to detect all classes of RF but probably detects mainly IgM. The presence of RF is not essential for the diagnosis of RA (so-called seronegative arthritis). RF also occurs in other autoimmune diseases (SLE, Scleroderma, Sjögrens) and in chronic infections (septicaemia, bacterial endocarditis)
Rheumatoid factor is thus a rather non-specific assay. Anti-CCP is much more sensitive and specific for rheumatoid arthritis.
Diagnosis of rheumatoid arthritis, differential diagnosis of rheumatic disease. However, the presence of rheumatoid factor does not mean rheumatoid arthritis. Patients with rheumatoid arthritis having high levels of rheumatoid factor generally have poorer prognosis, more severe progressive disease with greater joint and bone destruction and higher incidence of nodules and multisystem involvement. Rheumatoid factor levels are generally fairly constant in individual patients although during a long period of remission some reduction can occur.
Interpretation
The presence of rheumatoid factor does NOT mean rheumatoid arthritis . RFs are found in 80-90% patients with rheumatoid arthritis but also patients with SLE (15-30%); Sjögrens syndrome (80-100%); MCTD (50-60%) and systemic sclerosis (20-30%) amongst others. Patients with rheumatoid arthritis and high levels of rheumatoid factor generally have poorer prognosis, more severe progressive disease with greater joint and bone destruction and higher incidence of nodules and multisystem involvement. Rheumatoid factor levels are generally fairly constant in individual patients although during a long period of remission some reduction can occur. The levels do not in general correlate with disease activity. Low levels of rheumatoid factor are common in a wide range of autoimmune or infectious diseases especially those associated with hypergammaglobulinaemia including viral hepatitis, chronic liver disease, syphilis, sarcoidosis, leprosy, pulmonary fibrosis. High levels (> 400 IU/ml) are most common in Rheumatoid Arthritis and/or Sjögrens syndrome especially associated with vasculitis or cryoglobulinaemia. High levels can also be found in bacterial endocarditis where they fall after effective treatment.
Sample
Serum Separator Tube (SST)
Assay details
Nephelometry
Restrictions
Increased levels of lipids (lipaemia), haemoglobin (haemolysis), or the presence of icterus in the assay sample may affect the assay result.
Reference range
<20IU/mL
Assay range notes
Range 0-5000IU/ml
Turnaround time
5 – 7 days
Analysing laboratory
Immunology Lab, James Cook University Hospital, Marton Road, TS4 3BW
A normal, healthy amount of rheumatoid factor is less than 20 units per milliliter (<20 U/mL). Your provider might also refer to your test as being negative or positive. A negative result means you have a normal amount of RF in your blood. Positive means you have high levels of rheumatoid factor.
Rheumatoid factor results can be reported in titres (normal <1:20) but more commonly as units (normal <23 IU/ml but see local guidelines, as this may vary from laboratory to laboratory).
The reported sensitivity of RF in RA (ie, the proportion of patients with RA who are RF positive) ranges from 26 to 90 percent. A meta-analysis reported the overall sensitivity to be 69 percent (95% CI 65-73) [3].
A rheumatoid factor level over 100 is strongly associated with autoimmune diseases like RA. To compare, typical findings are less than 60 u/ml. In addition to RA, a high rheumatoid factor can also point to cancer, chronic infections, Sjögren's disease, bacterial endocarditis, or other autoimmune disorders.
Some doctors define normal RF levels as 0–20 units per milliliter (U/ml) of blood. On the other hand, one 2012 study designated the upper limit of regular levels as 25 U/ml . A person's risk of developing rheumatoid arthritis typically increases with their RF level.
A positive RF is strong confirmatory evidence of RA. In a patient with polyarthritis it has a sensitivity of 70% and a specificity of 80%. However, in an unselected population its predictive value is low (20%). Very high titres of RF are associated with severe disease and are a marker of poor prognosis.
A higher level of rheumatoid factor in your blood is closely linked with autoimmune diseases, especially rheumatoid arthritis. But a number of other diseases and conditions can raise rheumatoid factor levels, including: Cancer.Chronic infections, such as viral hepatitis B and C.
A few studies show that fish oil supplements may help symptoms of RA. A 2018 research review stated that omega-3 fatty acids, which are found in fish oil, reduced RA disease activity markers and inflammation markers.
Doctors say most patients do well on methotrexate alone, a drug that's been used for RA since the 1980s, and want to avoid the added expense and toxicity of unnecessary medications. Hydroxychloroquine is recommended over methotrexate for patients with low disease activity because it has fewer side effects.
It consists of a sum score of the four measures in the first definition plus a physician assessment. Because the definition of RA remission has been subjective in the past, published rates vary greatly, ranging from as little as 10% to more than 60%.
Rheumatoid factor (RF) is found commonly in patients with systemic lupus erythematosus (SLE), and has been associated with a more benign disease course. Anti-citrullinated peptide antibodies (ACPA) are more specific for rheumatoid arthritis (RA).
A higher level of rheumatoid factor in your blood is closely linked with autoimmune diseases, especially rheumatoid arthritis. But a number of other diseases and conditions can raise rheumatoid factor levels, including: Cancer. Chronic infections, such as viral hepatitis B and C.
What does a high RF value mean? The high value of the retention factor means the interaction between the compound of interest and the surface is strong. It also means that the compound of interest has a high solubility in the mobile phase.
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